Rename ‘up’ to ‘cloudup’ and update install instructions

[quinncomendant]

The npm package name up has been assumed by apex/up, thus cloudup-cli can no longer be installed with npm install -g up. I recommend cloudup-cli be renamed to cloudup so it can be installed with npm install -g cloudup and can be installed in parallel with the new up.

In the meantime, cloudup-cli can be installed by referencing the github repo directly, like this:

npm install -g Automattic/cloudup-cli

[kud]

+1

And: apex/up#549